Fiber optic dense wavelength division multiplexer utilizing a multi-stage parallel cascade method of wavelength separation

ABSTRACT

An improved dense wavelength division multiplexer for the separation of optical channels is provided. The dense wavelength division multiplexer includes the inputting of an optical signal with the optical signal containing a plurality of optical channels; the separating of one or more of the plurality of optical channels from the optical signal using separators at least partly arranged in a multi-stage parallel cascade configuration; and the outputting of the separated plurality of channels along a plurality of optical paths. The dense wavelength division multiplexer of the present invention provides for a lower insertion loss by requiring an optical signal to travel through fewer optical components in the separation process.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.09/130,386, entitled “Fiber Optic Dense Wavelength Division MultiplexerUtilizing a Multi-Stage Parallel Cascade Method of WavelengthSeparation,” filed on Aug. 6, 1998 now U.S. Pat. No. 6,263,126.

FIELD OF THE INVENTION

The present invention relates to fiber optic networks, and moreparticularly to fiber optic dense wavelength division multiplexers.

BACKGROUND OF THE INVENTION

Fiber optic networks are becoming increasingly popular for datatransmission due to their high speed, high capacity capabilities.Multiple wavelengths may be transmitted along the same optic fiber.These wavelengths are combined to provide a single transmitted signal. Acrucial feature of a fiber optic network is the separation of theoptical signal into its component wavelengths, or “channels”, typicallyby a dense wavelength division multiplexer. This separation must occurin order for the exchange of wavelengths between signals on “loops”within networks to occur. The exchange occurs at connector points, orpoints where two or more loops intersect for the purpose of exchangingwavelengths.

Add/drop systems exist at the connector points for the management of thechannel exchanges. The exchanging of data signals involves theexchanging of matching wavelengths from two different loops within anoptical network. In other words, each signal drops a channel to theother loop while simultaneously adding the matching channel from theother loop.

FIG. 1 illustrates a simplified optical network 100. A fiber opticnetwork 100 could comprise a main loop 150 which connects primarylocations, such as San Francisco and New York. In-between the primarylocations is a local loop 110 which connect with loop 150 at connectorpoint 140. Thus, if local loop 110 is Sacramento, wavelengths at SanFrancisco are multiplexed into an optical signal which will travel fromSan Francisco, add and drop channels with Sacramento's signal atconnector point 140, and the new signal will travel forward to New York.Within loop 110, optical signals would be transmitted to variouslocations within its loop, servicing the Sacramento area. Localreceivers (not shown) would reside at various points within the localloop 110 to convert the optical signals into the electrical signals inthe appropriate protocol format.

The separation of an optical signal into its component channels aretypically performed by a dense wavelength division multiplexer. FIG. 2illustrates add/drop systems 200 and 210 with dense wavelength divisionmultiplexers 220 and 230. An optical signal from Loop 110 (λ₁-λ_(n))enters its add/drop system 200 at node A (240). The signal is separatedinto its component channels by the dense wavelength division multiplexer220. Each channel is then outputted to its own path 250-1 through 250-n.For example, λ₁ would travel along path 250-1, λ₂ would travel alongpath 250-2, etc. In the same manner, the signal from Loop 150(λ₁′-λ_(n)′) enters its add/drop system 210 via node C (270). The signalis separated into its component channels by the wavelength divisionmultiplexer 230. Each channel is then outputted via its own path 280-1through 280-n. For example, λ₁′ would travel along path 280-1, λ₂′ wouldtravel along path 280-2, etc.

In the performance of an add/drop function, for example, λ₁ istransferred to path 280-1. It is combined with the others of Loop 150'schannels into a single new optical signal by the dense wavelengthdivision multiplexer 230. The new signal is then returned to Loop 150via node D (290). At the same time, λ₁′ is transferred to path 250-1from 280-1. It is combined with the others of Loop 110's channels into asingle optical signal by the dense wavelength division multiplexer 220.This new signal is then returned to Loop 110 via node B (260). In thismanner, from Loop 110's point of view, channel λ₁ of its own signal isdropped to Loop 150 while channel λ₁′ of the signal from Loop 150 isadded to form part of its new signal. The opposite is true from Loop150's point of view. This is the add/drop function.

Conventional methods used by dense wavelength division multiplexers inseparating an optical signal into its component channels includes theuse of filters and fiber gratings as separators. A “separator,” as theterm is used in this specification, is a unit of optical componentswhich separates one or more channels from an optical signal. Filtersallow a target channel to pass through while redirecting all otherchannels. Fiber gratings target a channel to be reflected while allother channels pass through. Both filters and fiber gratings are wellknown in the art and will not be discussed in further detail here. FIG.3 illustrates a conventional multi-stage serial cascade configuration ofseparators in a dense wavelength division multiplexer 300. In thisconventional method, each separator targets only one channel to befiltered/reflected and sent along a path. For example, an optical signalcontaining channels λ₁-λ_(n) is inputted into separator 310A, whichfilters/reflects channel λ₁ and send it along its own path 320-1. Theremaining channels λ₂-λ_(n) are sent to the next separator 310B, whichfilters/reflects channel 2 and sends it along its own path 320-2. Thiscontinues until each channel has been filtered/reflected and sent alongits own path. Thus, with this method, for N channels there are Nseparators.

FIG. 4 illustrates a conventional single stage parallel configuration ofseparators in a dense wavelength division multiplexer 400. In thisconventional method, the original optical signal containing λ₁-λ_(n)enters a signal splitter 410 which splits the signal onto N separatepaths, each split signal containing channels λ₁-λ_(n). Each of thesesplit signals is sent along a separate path 420-1 through 420-n. Eachsignal is then filtered or reflected by the separators 430A-430N tooutput one particular channel. For example, a split signal containingchannels λ₁-λ_(n) exits the splitter 410 onto path 420-1. The splitsignal enters separator 430A which filters/reflects channel λ₁ and sendsit along path 420-1. Another split signal containing λ₁-λ_(n) exitssplitter 410 onto path 420-2 and enters separator 430B. Separator 430Bfilters/reflects channel λ₂ and sends it along path 420-2. This processrepeats to separate each channel. Thus for N channels, there must be Nseparators plus a signal splitter.

A problem with the conventional configurations of separators above isthe resulting high insertion loss. Insertion loss is the attenuation ofan optical signal caused by the insertion of an optical component, suchas a connector, coupler, or filter. For the multi-stage serial cascadeconfiguration illustrated in FIG. 3, each time the optical signal goesthrough a separator 310A-310N an amount of insertion loss results. Forexample, if the optical signal in FIG. 3 has eight channels λ₁-λ₈ andeach component causes 1 dB of insertion loss. By the time λ₈ isseparated, it would have passed through eight separators. As would thussuffer 8 dB of insertion loss.

The same problem exists for the single stage parallel configuration inFIG. 4. Assume again that the optical signal contains eight channels andeach component causes 1 dB of insertion loss. In splitting one signalonto eight paths, a 9 dB insert loss results. Another 1 dB of loss isadded by the separator 430A-430N. Thus, each channel suffers 10 dB ofinsertion loss.

Therefore, there exists a need for a dense wavelength divisionmultiplexer with a method of separation which lowers insertion loss. Thepresent invention addresses such a need.

SUMMARY OF THE INVENTION

An improved dense wavelength division multiplexer for the separation ofoptical channels is provided. The dense wavelength division multiplexerincludes the inputting of an optical signal with the optical signalcontaining a plurality of optical channels; the separating of one ormore of the plurality of optical channels from the optical signal usingseparators at least partly arranged in a multi-stage parallel cascadeconfiguration; and the outputting of the separated plurality of channelsalong a plurality of optical paths. The dense wavelength divisionmultiplexer of the present invention provides for a lower insertion lossby requiring an optical signal to travel through fewer opticalcomponents in the separation process.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is an illustration of a simplified optical network.

FIG. 2 is an illustration of conventional add/drop systems and densewavelength division multiplexers.

FIG. 3 is an illustration of a conventional multi-stage serial cascadeconfiguration of separators.

FIG. 4 is an illustration of a conventional single stage parallelconfiguration of separators.

FIGS. 5A and 5B are simple block diagrams of a first preferredembodiment of a dense wavelength division multiplexer in accordance withthe present invention.

FIG. 6 is an illustration of a second preferred embodiment of a densewavelength division multiplexer in accordance with the presentinvention.

FIG. 7 is an illustration of a third preferred embodiment of a densewavelength division multiplexer in accordance with the presentinvention.

FIG. 8 is an illustration of a fourth preferred embodiment of a densewavelength division multiplexer in accordance with the presentinvention.

FIG. 9 is a block diagram of a first embodiment of a separator which maybe used with the present invention.

FIG. 10 is a block diagram of a second embodiment of separator which maybe used with the present invention.

FIG. 11 is a block diagram of the first embodiment of a separatorperforming the add/drop function in accordance with the presentinvention.

FIG. 12 is a block diagram of the second embodiment of a separatorperforming the add/drop function in accordance with the presentinvention.

DETAILED DESCRIPTION

The present invention relates to an improvement in a dense wavelengthdivision multiplexer. The following description is presented to enableone of ordinary skill in the art to make and use the invention and isprovided in the context of a patent application and its requirements.Various modifications to the preferred embodiment will be readilyapparent to those skilled in the art and the generic principles hereinmay be applied to other embodiments. Thus, the present invention is notintended to be limited to the embodiment shown but is to be accorded thewidest scope consistent with the principles and features describedherein.

A dense wavelength division multiplexer (DWDM) in accordance with thepresent invention provides for a lower insertion loss by requiring anoptical signal to travel through fewer optical components. To moreparticularly describe the features of the present invention, pleaserefer to FIGS. 5A through 14 in conjunction with the discussion below.

FIG. 5A is a simple block diagram of a first preferred embodiment of aDWDM with a multi-stage parallel cascade configuration of separators inaccordance with the present invention. An optic signal containingchannels λ₁-λ_(n) enters the DWDM 500 through node A (240). The signalpasses through a separator 510A. The separator 510A divides the signalinto two separate signals, one containing the odd channels (λ₁, λ₃, λ₅,. . . ) (530) and the other containing the even channels (λ₂, λ₄, λ₆, .. . ) (540), i.e., every other channel. These odd and even channels areeach passed through another separator 510B-510C which further dividesthem by every other channel. This division continues until only onechannel is outputted to each optic fiber, 250-1 through 250-n.

This multi-stage parallel cascade configuration of separators reducesthe amount of insertion loss typically suffered with the conventionalconfigurations because it reduces the number of components through whichan optical signal must travel. For example, as illustrated in FIG. 5B,if an optical signal contains eight wavelengths λ₁-λ₈, only sevenseparators 510A-510G are used. Assume that each separator causes 1 dB ofinsertion loss. Since each channel only goes through three separators,they only suffer 3 dB of insertion loss, much less than the 8 dB and 10dB of the conventional multi-stage serial and single stage parallelconfigurations respectively. The relationship between the number ofstage M and the number of separators N for the DWDM 500 of the presentinvention is N=2^(M). M is much smaller than N, thus the DWDM 500 of thepresent invention has lower insertion loss than both conventionalconfigurations.

FIG. 6 illustrates a second preferred embodiment of a DWDM in accordancewith the present invention. This DWDM 600 has a hybrid parallel-serialcascade configuration. Certain stages of the DWDM uses a parallelcascade configuration of separators as described in conjunction withFIGS. 5A and 5B above. Along with these parallel cascade stages arestages which use a serial cascade configuration of separators. Forexample, stages 1 and 2 in the DWDM 600 uses a parallel cascadeconfiguration while stage 3 uses a serial cascade configuration. Assumethat an optical signal containing channels λ₁-λ₁₆ is input into the DWDM600. Separator 610A separates them into two signals, one containing theodd channels (λ₁, λ₃, . . . λ₁₅), the other containing the even channels(λ₂, λ₄, . . . λ₁₆). The odd channels are input into separator 610Bwhich separates them further into two sets. One set of signals (λ₁, λ₅,. . . λ₁₃) is input into separator 620A, while the other set (λ₃, λ₇, .. . λ₁₅) is input into separator 620B. The even channels are input intoseparator 610C which separates them further into sets of signals. Oneset of signals (λ₂, λ₆, . . . λ₁₄) is input into separator 620C, whilethe other set (λ₄, λ₉, . . . λ₁₆) input into separator 620D. Separators620A-620D are in a serial cascade configuration which filters for eachindividual channel and outputs each onto separate paths. By using thishybrid configuration, a user has more flexibility in deciding how manyseparators will be used. This can be important when costs is aparticular concern to a user.

FIG. 7 illustrates a third embodiment of a DWDM in accordance with thepresent invention. This DWDM 700 has a programmable router configurationwhich adds programmability to the parallel cascade configurationillustrated in FIGS. 5A and 5B. In this embodiment, the separators(710A-710G) may be programmed to route particular channels to particularpaths and therefore function as 1×2 switches. For example, assume thatan optical signal containing channels λ₁-λ₈ is input into the DWDM 700.Separator 710A is programmed to route the odd channels (λ₁, λ₃, λ₅, λ₇)to separator 710B and the even channels (λ₂, λ₄, λ₆, λ₈) to separator710C, as with the embodiment illustrated in FIG. 5B. Separator 710B isprogrammed to route λ₁ and λ₅ to separator 710D, and λ₃ and λ₇ toseparator 710F. However, separator 710C is programmed to flip the routeof the wavelengths, represented by the “1”, such that λ₆ and λ₈ arerouted to 710F instead of 710G, and λ₂ and λ₄ are routed to 710G insteadof 710F. Similarly, separators 710D and 710G are programmed not to flipthe route of the wavelengths while separators 710E and 710F are,resulting in the outputs as shown. Comparing the outputs with theoutputs in FIG. 5B, one can see the rerouting of λ₃, λ₇, λ₂, λ₄, and λ₈.

FIG. 8 illustrates a fourth embodiment of a DWDM in accordance with thepresent invention. This DWDM 800 also contains separators which functionas 2×2 switches, as with the programmable router configuration of FIG.7. However, in this embodiment, these separators are used to perform theadd/drop function. For example, assume an optical signal containingwavelengths λ₁-λ₈ in input into the DWDM 800. Separator 810A separatesthis signal into its odd (λ₁, λ₃, λ₅, λ₇) and even (λ₂, λ₄, λ₆, λ₈)channels. The odd channels are input into separator 810B, which furtherseparates them into two sets of channels, (λ₁, λ₅) and (λ₃, λ₇). The(λ₃, λ₇) set of channels are input into separator 810C which separatesthem into separate channels λ₃ and λ₇. Channel λ₃ is then dropped. To beadded is channel λ₃′ which is inputted into separator 810C. Acting as a2×2 switch as described with the second embodiment above, channel λ₃′ isthen added to λ₇ by the separator 810C. This signal is looped back as aninput to separator 810B, which adds λ₇ and λ₃′ to λ₁ and λ₅. Thiscombined signal is looped back as an input to separator 810A, which addschannels λ₁, λ₅λ₇, λ₃′ to channels λ₂, λ₄, λ₆, λ₈, resulting in oneoptical signal containing channels λ₁, λ₃′, λ₄, λ₅, λ₆, λ₇, and λ₈. Thisnew signal is then the output of the DWDM 800. Thus, in this manner,channel λ₃ is dropped while channel λ₃′ is added. For this embodiment,for every three stages, one channel may be dropped from a group of eightchannels. More generally, for 2^(n) channels and m stages, 2^(n-m)channels may be dropped.

Separators which may be used with the multi-stage parallel cascadeconfiguration of the present invention are disclosed in co-pending U.S.Patent Applications “Fiber Optic Dense Wavelength Division Multiplexerwith a Phase Differential Method of Wavelength Separation Utilizing aPolarization Beam Splitter and a Nonlinear Interferometer”, Ser. No.09/696,108, filed on Oct. 24, 2000, and in U.S. Pat. Nos. 6,130,971,6,169,828, and 6,215,926 all assigned to the assignee of the presentapplication. Applicant hereby incorporates these co-pending applicationsand U.S. Patents by reference.

FIG. 9 illustrates one embodiment of a separator which may be used withthe present invention. This embodiment is disclosed in U.S. Pat. No.6,215,926. The separator 900 comprises an input fiber 930 for inputtingan optical signal, and two output fibers 940 and 960. It also comprisestwo blocks of glass 910A-910B, where the index of refraction for glassblock 910A is greater than the index of refraction for glass block 910B,placed directly next to each other. Adjacent to one side of the blocks910A and 910B is a nonlinear interferometer 950 which introduces a phasedifference into the even channels while maintaining the same phase forthe odd channels. At the place where the two blocks 910A-910B meet, theglass is coated with a reflective coating 920 with a reflectivity, forexample, of 50%.

The reflective coating 920 splits the optical signal containing λ1-λninto at least two portions 962, 964. According to the general operationof beam splitters, when light travels through glass block 910B and thenis reflected from a surface of glass block 910A (which has a greaterindex of refraction than glass block 910B), the light undergoes a πphase shift. This π phase shift is indicated in FIG. 9 by the negativesign of the electric field (−E1) associated with signal 962 after it isreflected at the 50% reflective coating 920. Otherwise, the light doesnot undergo a phase shift, as is indicated by the positive sign of theelectric field (E2) associated with signal 964 after it is transmittedthrough the 50% reflective coating 920 in FIG. 9. This reflection phaseflip is very well known in the art and will not be further describedhere. In the preferred embodiment, the reflective coating 920 ispolarization insensitive. The nonlinear interferometer 950 thenintroduces a π phase difference into the even channels while maintainingthe phase of the odd channels. The two output fibers 940 and 960 arethen aligned, or placed at a particular distance from the separator 900,such that even channels are captured in phase in one fiber while the oddchannels are captured in phase in the other. An example of a nonlinearinterferometer which may be used with the separator 900 is disclosed inU.S. Pat. No. 6,169,604, assigned to the assignee of the presentapplication. Applicant hereby incorporates this U.S. Patent byreference.

FIG. 10 is a simple block diagram of a second embodiment of a separatorwhich may be used with the present invention. This embodiment isdisclosed in U.S. Pat. Nos. 6,130,971 and 6,169,828, assigned theassignee of the present application. FIG. 10 shows a separator 1000comprising an optic fiber 1010 for inputting an optical signal. Thesignal passes through a lens 1050. It travels into a polarization beamsplitter 1070 which splits the signal based on its polarization. Theportion of the signal parallel to a plane in the splitter 1070 (Ssignal) is reflected toward an interferometer 1050A. The portion of thesignal perpendicular to the plane in the splitter 1070 (P signal) passesthrough toward an interferometer 1050B. The interferometers 1050A and1050B introduce phase differences in the even channels but not the oddchannels. An example of interferometer 1050A and 1050B are alsodisclosed in U.S. Pat. Nos. 6,169,604 and 6,130,971.

FIGS. 11 and 12 illustrate the two embodiments of separators of FIGS. 9and 10 respectively, performing the add/drop function as described inconjunction with the DWDM of FIGS. 7 and 8. In each embodimentillustrated in FIGS. 11 and 12, an additional input fiber (1110 of FIG.11 and 1210 of FIG. 12) is added to input a second optical signal. Theseembodiments performing the add/drop function are also disclosed in theirrespective co-pending U.S. applications.

A dense wavelength division multiplexer with a multi-stage parallelcascade configuration of channel separators has been disclosed. Thisconfiguration provides for a lower insertion loss by requiring anoptical signal to travel through fewer optical components.

Although the multistage parallel configuration of the present inventionhas been described with the specific embodiments of the separators, oneof ordinary skill in the art will understand that other separators maybe used with the configuration of the present invention withoutdeparting from the spirit and scope of the present invention.

Although the present invention has been described in accordance with theembodiments shown, one of ordinary skill in the art will readilyrecognize that there could be variations to the embodiments and thosevariations would be within the spirit and scope of the presentinvention. Accordingly, many modifications may be made by one ofordinary skill in the art without departing from the spirit and scope ofthe appended claims.

What is claimed is:
 1. A method for separating an optical signal intooptical channels, the method comprising the steps of: (a) inputting theoptical signal, the optical signal comprising a plurality of opticalchannels; (b) separating one or more of the plurality of opticalchannels into a first set of channels and a second set of channelsinterleaved with the first set of channels from the optical signal usinga plurality of separators, wherein the separators are at least partlyarranged in a multi-stage parallel cascade configuration; and (c)outputting the separated plurality of channels along a plurality ofoptical paths, wherein at least one of the plurality of separatorsoutputs a first set of the plurality of optical channels to a firstoutput, wherein at least one of the plurality of separators outputs asecond set of the plurality of optical channels to a second output,wherein the first set of the plurality of optical channels isinterleaved with the second set of the plurality of optical channels. 2.The method of claim 1, wherein the separators of the separating step (b)are arranged completely in a multi-stage parallel cascade configuration.3. The method of claim 1, wherein the separators of the separating step(b) are arranged in a hybrid parallel-serial cascade configuration. 4.The method of claim 1, wherein the separators of the separating step (b)are arranged in a programmable router configuration.
 5. The method ofclaim 1, wherein the separators of the separating step (b) are arrangedin a programmable configuration performing the add/drop function.
 6. Themethod of claim 1, wherein the optical signal in step (b) is separatedinto a set of odd optical channels and a set of even optical signals. 7.The method of claim 1, wherein the separator comprises: (a) a firstglass block coupled to a second glass block, wherein the first glassblock is optically coupled to the inputted optical signal; (b) at leastone reflective coating residing between the first and second glassblocks; and (c) a split beam interferometer optically coupled to thefirst and second glass blocks, wherein the interferometer introduces aphase difference between at least two of the plurality of opticalchannels.
 8. The method of claim 1, wherein the separator comprises: (a)at least one lens optically coupled to the inputted optical signal; (b)at least one lens optically coupled to the outputted plurality ofoptical channels; (c) a polarization beam splitter optically coupled tothe lenses; and (d) at least two reflection interferometers opticallycoupled to the polarization beam splitter, wherein the interferometersintroduce a phase difference between at least two of the plurality ofoptical channels.
 9. A system for separating an optical signal intooptical channels, the system comprising: means for inputting the opticalsignal, the optical signal comprising a plurality of optical channels; aplurality of separators for separating one or more of the plurality ofoptical channels from the optical signal, wherein the separating meansis at least partly arranged in a multi-stage parallel cascadeconfiguration; and means for outputting the separated plurality ofchannels along a plurality of optical paths, wherein at least one of theplurality of separators outputs a first set of the plurality of opticalchannels to a first output, wherein at least one of the plurality ofseparators outputs a second set of the plurality of optical channels toa second output, wherein the first set of the plurality of opticalchannels is interleaved with the second set of the plurality of opticalchannels.
 10. The system of claim 9, wherein the separators of theseparating means are arranged completely in a multi-stage parallelcascade configuration.
 11. The system of claim 9, wherein the separatorsof the separating means are arranged in a hybrid parallel-serial cascadeconfiguration.
 12. The system of claim 9, wherein the separators of theseparating means are arranged in a programmable router configuration.13. The system of claim 9, wherein the separators of the separatingmeans are arranged in a programmable configuration performing theadd/drop function.
 14. The system of claim 9, wherein the optical signalin the separating means is separated into a set of odd optical channelsand a set of even optical signals.
 15. The system of claim 9, whereinthe separating means comprises: (a) a first glass block coupled to asecond glass block, wherein the first glass block is optically coupledto the inputting means; (b) at least one reflective coating residingbetween the first and second glass blocks; and (c) a split beaminterferometer optically coupled to the first and second glass blocks,wherein the interferometer introduces a phase difference between atleast two of the plurality of optical channels.
 16. The system of claim9, wherein the separating means comprises: (a) at least one lensoptically coupled to the inputting means; (b) at least one lensoptically coupled to the outputting means; (c) a polarization beamsplitter optically coupled to the lenses; and (d) at least tworeflection interferometers optically coupled to the polarization beamsplitter, wherein the interferometers introduce a phase differencebetween at least two of the plurality of optical channels.
 17. Themethod of claim 2, wherein the multi-stage parallel cascadeconfiguration comprises: a plurality of cascades occurring in parallel,wherein each cascade comprises some of the plurality of separatorsarranged in at least one stage, wherein each separator derives from oracts upon a product of a preceding stage.
 18. The method of claim 3,wherein the hybrid parallel-serial cascade configuration comprises: aplurality of cascades occurring in parallel, wherein each cascadecomprises some of the plurality of separators arranged in a plurality ofstages, wherein a first stage of the plurality of stages of one of theplurality of cascades is arranged in a parallel cascade configuration,wherein each of the separators in the first stage derives from or actsupon a product of a preceding stage, wherein a second stage of theplurality of stages of the one of the plurality of cascades is arrangedin a serial cascade configuration, wherein the second stage is opticallycoupled to the first stage, wherein the separators in the second stageare optically coupled in series.
 19. The method of claim 4, wherein theprogrammable router configuration comprises: the plurality of separatorsconfigured in either a multi-stage parallel cascade configuration or ahybrid parallel-serial cascade configuration, wherein at least one ofthe plurality of separators may be programmed such that a particularchannel of the plurality of channels is routed to a particular opticalpath of the plurality of optical paths.
 20. The method of claim 19,wherein the multi-stage parallel cascade configuration comprises: aplurality of cascades occurring in parallel, wherein each cascadecomprises some of the plurality of separators arranged in at least onestage, wherein each separator derives from or acts upon a product of apreceding stage.
 21. The method of claim 19, wherein the hybridparallel-serial cascade configuration comprises: a plurality of cascadesoccurring in parallel, wherein each cascade comprises some of theplurality of separators arranged in a plurality of stages, wherein afirst stage of the plurality of stages of one of the plurality ofcascades is arranged in a parallel cascade configuration, wherein eachof the separators in the first stage derives from or acts upon a productof a preceding stage, wherein a second stage of the plurality of stagesof the one of the plurality of cascades is arranged in a serial cascadeconfiguration, wherein the second stage is optically coupled to thefirst stage, wherein the separators in the second stage are opticallycoupled in series.
 22. The method of claim 5, wherein the programmableconfiguration performing the add/drop function comprises: a firstseparator, comprising: a first input port of the first separator, asecond input port of the first separator, a first output port of thefirst separator, and a second output port of the first separator; and asecond separator, comprising: a first input port of the second separatoroptically coupled to the second output port of the first separator, asecond input port of the second separator, a first output port of thesecond separator optically coupled to the second input port of the firstseparator, and a second output port of the second separator.
 23. Thesystem of claim 10, wherein the multi-stage parallel cascadeconfiguration comprises: a plurality of cascades occurring in parallel,wherein each cascade comprises some the separators of the separatingmeans arranged in at least one stage, wherein each separator derivesfrom or acts upon a product of a preceding stage.
 24. The system ofclaim 11, wherein the hybrid parallel-serial cascade configurationcomprises: a plurality of cascades occurring in parallel, wherein eachcascade comprises some of the separators of the separating meansarranged in a plurality of stages, wherein a first stage of theplurality of stages of one of the plurality of cascades is arranged in aparallel cascade configuration, wherein each of the separators in thefirst stage derives from or acts upon a product of a preceding stage,wherein a second stage of the plurality of stages of the one of theplurality of cascades is arranged in a serial cascade configuration,wherein the second stage is optically coupled to the first stage,wherein the separators in the second stage are optically coupled inseries.
 25. The system of claim 12, wherein the programmable routerconfiguration comprises: the separators of the separating meansconfigured in either a multi-stage parallel cascade configuration or ahybrid parallel-serial cascade configuration, wherein at least one ofthe separators may be programmed such that a particular channel of theplurality of channels is routed to a particular optical path of theplurality of optical paths.
 26. The system of claim 25, wherein themulti-stage parallel cascade configuration comprises: a plurality ofcascades occurring in parallel, wherein each cascade comprises some ofthe separators of the separating means arranged in at least one stage,wherein each separator derives from or acts upon a product of apreceding stage.
 27. The system of claim 25, wherein the hybridparallel-serial cascade configuration comprises: a plurality of cascadesoccurring in parallel, wherein each cascade comprises some of theseparators of the separating means arranged in a plurality of stages,wherein a first stage of the plurality of stages of one of the pluralityof cascades is arranged in a parallel cascade configuration, whereineach of the separators in the first stage derives from or acts upon aproduct of a preceding stage, wherein a second stage of the plurality ofstages of the one of the plurality of cascades is arranged in a serialcascade configuration, wherein the second stage is optically coupled tothe first stage, wherein the separators in the second stage areoptically coupled in series.
 28. The system of claim 13, wherein theprogrammable configuration performing the add/drop function comprises: afirst separator, comprising: a first input port of the first separator,a second input port of the first separator, a first output port of thefirst separator, and a second output port of the first separator; and asecond separator, comprising: a first input port of the second separatoroptically coupled to the second output port of the first separator, asecond input port of the second separator, a first output port of thesecond separator optically coupled to the second input port of the firstseparator, and a second output port of the second separator.
 29. Amethod for separating an optical signal into optical channels, themethod comprising the steps of: (a) inputting the optical signal, theoptical signal comprising a plurality of optical channels; (b)separating one or more of the plurality of optical channels from theoptical signal using a plurality of separators, wherein the separatorsare at least partly arranged in a multi-stage parallel cascadeconfiguration, wherein at least one separator comprises: a first glassblock coupled to a second glass block, wherein the first glass block isoptically coupled to the inputted optical signal, at least onereflective coating residing between the first and second glass blocks,and a split beam interferometer optically coupled to the first andsecond glass blocks, wherein the interferometer introduces a phasedifference between at least two of the plurality of optical channels;and (c) outputting the separated plurality of channels along a pluralityof optical paths.
 30. A method for separating an optical signal intooptical channels, the method comprising the steps of: (a) inputting theoptical signal, the optical signal comprising a plurality of opticalchannels; (b) separating one or more of the plurality of opticalchannels from the optical signal using a plurality of separators,wherein the separators are at least partly arranged in a multi-stageparallel cascade configuration, wherein at least one separatorcomprises: at least one lens optically coupled to the inputted opticalsignal, at least one lens optically coupled to the outputted pluralityof optical channels, a polarization beam splitter optically coupled tothe lenses, and at least two reflection interferometers opticallycoupled to the polarization beam splitter, wherein the interferometersintroduce a phase difference between at least two of the plurality ofoptical channels; and (c) outputting the separated plurality of channelsalong a plurality of optical paths.
 31. A system for separating anoptical signal into optical channels, the system comprising: means forinputting the optical signal, the optical signal comprising a pluralityof optical channels; means for separating one or more of the pluralityof optical channels from the optical signal, wherein the separatingmeans is at least partly arranged in a multi-stage parallel cascadeconfiguration, wherein the separating means comprises: a first glassblock coupled to a second glass block, wherein the first glass block isoptically coupled to the inputting means, at least one reflectivecoating residing between the first and second glass blocks, and a splitbeam interferometer optically coupled to the first and second glassblocks, wherein the interferometer introduces a phase difference betweenat least two of the plurality of optical channels; and means foroutputting the separated plurality of channels along a plurality ofoptical paths.
 32. A system for separating an optical signal intooptical channels, the system comprising: means for inputting the opticalsignal, the optical signal comprising a plurality of optical channels;means for separating one or more of the plurality of optical channelsfrom the optical signal, wherein the separating means is at least partlyarranged in a multi-stage parallel cascade configuration, wherein theseparating means comprises: at least one lens optically coupled to theinputting means, at least one lens optically coupled to the outputtingmeans, a polarization beam splitter optically coupled to the lenses, andat least two reflection interferometers optically coupled to thepolarization beam splitter, wherein the interferometers introduce aphase difference between at least two of the plurality of opticalchannels; and means for outputting the separated plurality of channelsalong a plurality of optical paths.
 33. A method for separating anoptical signal into optical channels, the method comprising the stepsof: (a) inputting the optical signal, the optical signal comprising aplurality of optical channels; (b) separating one or more of theplurality of optical channels from the optical signal using a pluralityof separators, wherein at least one of the plurality of separators isconfigured as a 1×2 switch, wherein the separators are at least partlyarranged in a multi-stage parallel cascade configuration, wherein theseparators are arranged completely in a multi-stage parallel cascadeconfiguration; and (c) outputting the separated plurality of channelsalong a plurality of optical paths.
 34. The method of claim 33, whereinthe multi-stage parallel cascade configuration comprises: a plurality ofcascades occurring in parallel, wherein each cascade comprises some ofthe plurality of separators arranged in at least one stage, wherein eachseparator derives from or acts upon a product of a preceding stage. 35.A method for separating an optical signal into optical channels, themethod comprising the steps of: (a) inputting the optical signal, theoptical signal comprising a plurality of optical channels; (b)separating one or more of the plurality of optical channels from theoptical signal using a plurality of separators, wherein at least one ofthe plurality of separators is configured as a 1×2 switch, wherein theseparators are at least partly arranged in a multi-stage parallelcascade configuration, wherein the separators are arranged in a hybridparallel-serial cascade configuration; and (c) outputting the separatedplurality of channels along a plurality of optical paths.
 36. The methodof claim 35, wherein the hybrid parallel-serial cascade configurationcomprises: a plurality of cascades occurring in parallel, wherein eachcascade comprises some of the plurality of separators arranged in aplurality of stages, wherein a first stage of the plurality of stages ofone of the plurality of cascades is arranged in a parallel cascadeconfiguration, wherein each of the separators in the first stage derivesfrom or acts upon a product of a preceding stage, wherein a second stageof the plurality of stages of the one of the plurality of cascades isarranged in a serial cascade configuration, wherein the second stage isoptically coupled to the first stage, wherein the separators in thesecond stage are optically coupled in series.
 37. A method forseparating an optical signal into optical channels, the methodcomprising the steps of: (a) inputting the optical signal, the opticalsignal comprising a plurality of optical channels; (b) separating one ormore of the plurality of optical channels from the optical signal usinga plurality of separators, wherein at least one of the plurality ofseparators is configured as a 1×2 switch, wherein the separators are atleast partly arranged in a multi-stage parallel cascade configuration,wherein the separators are arranged in a programmable routerconfiguration; and (c) outputting the separated plurality of channelsalong a plurality of optical paths.
 38. The method of claim 37, whereinthe programmable router configuration comprises: the plurality ofseparators configured in either a multi-stage parallel cascadeconfiguration or a hybrid parallel-serial cascade configuration, whereinat least one of the plurality of separators may be programmed such thata particular channel of the plurality of channels is routed to aparticular optical path of the plurality of optical paths.
 39. Themethod of claim 38, wherein the multi-stage parallel cascadeconfiguration comprises: a plurality of cascades occurring in parallel,wherein each cascade comprises some of the plurality of separatorsarranged in at least one stage, wherein each separator derives from oracts upon a product of a preceding stage.
 40. The method of claim 38,wherein the hybrid parallel-serial cascade configuration comprises: aplurality of cascades occurring in parallel, wherein each cascadecomprises some of the plurality of separators arranged in a plurality ofstages, wherein a first stage of the plurality of stages of one of theplurality of cascades is arranged in a parallel cascade configuration,wherein each of the separators in the first stage derives from or actsupon a product of a preceding stage, wherein a second stage of theplurality of stages of the one of the plurality of cascades is arrangedin a serial cascade configuration, wherein the second stage is opticallycoupled to the first stage, wherein the separators in the second stageare optically coupled in series.
 41. A method for separating an opticalsignal into optical channels, the method comprising the steps of: (a)inputting the optical signal, the optical signal comprising a pluralityof optical channels; (b) separating one or more of the plurality ofoptical channels from the optical signal using a plurality ofseparators, wherein at least one of the plurality of separators isconfigured as a 1×2 switch, wherein the separators are at least partlyarranged in a multi-stage parallel cascade configuration, wherein theoptical signal is separated into a set of odd optical channels and a setof even optical signals; and (c) outputting the separated plurality ofchannels along a plurality of optical paths.
 42. A method for separatingan optical signal into optical channels, the method comprising the stepsof: (a) inputting the optical signal, the optical signal comprising aplurality of optical channels; (b) separating one or more of theplurality of optical channels from the optical signal using a pluralityof separators, wherein at least one of the plurality of separators isconfigured as a 1×2 switch, wherein the separators are at least partlyarranged in a multi-stage parallel cascade configuration, wherein atleast one of the separators comprises: a first glass block coupled to asecond glass block, wherein the first glass block is optically coupledto the inputted optical signal, at least one reflective coating residingbetween the first and second glass blocks, and a split beaminterferometer optically coupled to the first and second glass blocks,wherein the interferometer introduces a phase difference between atleast two of the plurality of optical channels; and (c) outputting theseparated plurality of channels along a plurality of optical paths. 43.A method for separating an optical signal into optical channels, themethod comprising the steps of: (a) inputting the optical signal, theoptical signal comprising a plurality of optical channels; (b)separating one or more of the plurality of optical channels from theoptical signal using a plurality of separators, wherein at least one ofthe plurality of separators is configured as a 1×2 switch, wherein theseparators are at least partly arranged in a multi-stage parallelcascade configuration, wherein at least one of the separators comprises:at least one lens optically coupled to the inputted optical signal, atleast one lens optically coupled to the outputted plurality of opticalchannels, a polarization beam splitter optically coupled to the lenses,and at least two reflection interferometers optically coupled to thepolarization beam splitter, wherein the interferometers introduce aphase difference between at least two of the plurality of opticalchannels; and (c) outputting the separated plurality of channels along aplurality of optical paths.
 44. A system for separating an opticalsignal into optical channels, the system comprising: means for inputtingthe optical signal, the optical signal comprising a plurality of opticalchannels; means for separating one or more of the plurality of opticalchannels from the optical signal, wherein the separating means comprisesat least one 1×2 switch, wherein separators of the separating means arearranged completely in a multi-stage parallel cascade configuration; andmeans for outputting the separated plurality of channels along aplurality of optical paths.
 45. The system of claim 44, wherein themulti-stage parallel cascade configuration comprises: a plurality ofcascades occurring in parallel, wherein each cascade comprises some theseparators of the separating means arranged in at least one stage,wherein each separator derives from or acts upon a product of apreceding stage.
 46. A system for separating an optical signal intooptical channels, the system comprising: means for inputting the opticalsignal, the optical signal comprising a plurality of optical channels;means for separating one or more of the plurality of optical channelsfrom the optical signal, wherein the separating means is at least partlyarranged in a multi-stage parallel cascade configuration, wherein theseparating means comprises at least one 1×2 switch, wherein separatorsof the separating means are arranged in a hybrid parallel-serial cascadeconfiguration; and means for outputting the separated plurality ofchannels along a plurality of optical paths.
 47. The system of claim 46,wherein the hybrid parallel-serial cascade configuration comprises: aplurality of cascades occurring in parallel, wherein each cascadecomprises some of the separators of the separating means arranged in aplurality of stages, wherein a first stage of the plurality of stages ofone of the plurality of cascades is arranged in a parallel cascadeconfiguration, wherein each of the separators in the first stage derivesfrom or acts upon a product of a preceding stage, wherein a second stageof the plurality of stages of the one of the plurality of cascades isarranged in a serial cascade configuration, wherein the second stage isoptically coupled to the first stage, wherein the separators in thesecond stage are optically coupled in series.
 48. A system forseparating an optical signal into optical channels, the systemcomprising: means for inputting the optical signal, the optical signalcomprising a plurality of optical channels; means for separating one ormore of the plurality of optical channels from the optical signal,wherein the separating means is at least partly arranged in amulti-stage parallel cascade configuration, wherein the separating meanscomprises at least one 1×2 switch, wherein separators of the separatingmeans are arranged in a programmable router configuration; and means foroutputting the separated plurality of channels along a plurality ofoptical paths.
 49. The system of claim 48, wherein the programmablerouter configuration comprises: the separators of the separating meansconfigured in either a multi-stage parallel cascade configuration or ahybrid parallel-serial cascade configuration, wherein at least one ofthe separators may be programmed such that a particular channel of theplurality of channels is routed to a particular optical path of theplurality of optical paths.
 50. The system of claim 49, wherein themulti-stage parallel cascade configuration comprises: a plurality ofcascades occurring in parallel, wherein each cascade comprises some ofthe separators of the separating means arranged in at least one stage,wherein each separator derives from or acts upon a product of apreceding stage.
 51. The system of claim 49, wherein the hybridparallel-serial cascade configuration comprises: a plurality of cascadesoccurring in parallel, wherein each cascade comprises some of theseparators of the separating means arranged in a plurality of stages,wherein a first stage of the plurality of stages of one of the pluralityof cascades is arranged in a parallel cascade configuration, whereineach of the separators in the first stage derives from or acts upon aproduct of a preceding stage, wherein a second stage of the plurality ofstages of the one of the plurality of cascades is arranged in a serialcascade configuration, wherein the second stage is optically coupled tothe first stage, wherein the separators in the second stage areoptically coupled in series.
 52. A system for separating an opticalsignal into optical channels, the system comprising: means for inputtingthe optical signal, the optical signal comprising a plurality of opticalchannels; means for separating one or more of the plurality of opticalchannels from the optical signal, wherein the separating means is atleast partly arranged in a multi-stage parallel cascade configuration,wherein the separating means comprises at least one 1×2 switch, whereinthe optical signal in the separating means is separated into a set ofodd optical channels and a set of even optical signals; and means foroutputting the separated plurality of channels along a plurality ofoptical paths.
 53. A system for separating an optical signal intooptical channels, the system comprising: means for inputting the opticalsignal, the optical signal comprising a plurality of optical channels;means for separating one or more of the plurality of optical channelsfrom the optical signal, wherein the separating means is at least partlyarranged in a multi-stage parallel cascade configuration, wherein theseparating means comprises at least one 1×2 switch, wherein theseparating means comprises: a first glass block coupled to a secondglass block, wherein the first glass block is optically coupled to theinputting means, at least one reflective coating residing between thefirst and second glass blocks, and a split beam interferometer opticallycoupled to the first and second glass blocks, wherein the interferometerintroduces a phase difference between at least two of the plurality ofoptical channels; and means for outputting the separated plurality ofchannels along a plurality of optical paths.
 54. A system for separatingan optical signal into optical channels, the system comprising: meansfor inputting the optical signal, the optical signal comprising aplurality of optical channels; means for separating one or more of theplurality of optical channels from the optical signal, wherein theseparating means is at least partly arranged in a multi-stage parallelcascade configuration, wherein the separating means comprises at leastone 1×2 switch, wherein the separating means comprises: at least onelens optically coupled to the inputting means, at least one lensoptically coupled to the outputting means, a polarization beam splitteroptically coupled to the lenses, and at least two reflectioninterferometers optically coupled to the polarization beam splitter,wherein the interferometers introduce a phase difference between atleast two of the plurality of optical channels; and means for outputtingthe separated plurality of channels along a plurality of optical paths.